This invention relates to the field of deflectable tip instruments and, more particularly, to an active counterforce handle for use in such instruments to counter a return to center force generated by an instrument shaft upon being deflected.
Modern surgical procedures often necessitate localized diagnosis, or treatments applied to relatively inaccessible interior areas of the body. In the past, such procedures have typically involved invasive surgery, enabling the physician to visually identify or treat the area of interest by accessing a relatively large opening or incision made in the body. Unfortunately, invasive surgical methods often include undesirable side-effects, from the tissue trauma associated with the procedure. Often, the effects of the trauma prolong the healing and rehabilitation period for the patient.
To minimize the trauma often associated with invasive surgery, those skilled in the art have developed relatively small surgical instrument, such as catheters, for insertion into the vasculature of the body. Typically, the particular surgical instrument accesses the body through a small incision made near the skin, where it can then be advanced to an area of interest. However, in order to navigate through the vasculature in a predictable manner, the instrument must be precisely controllable to position, as examples, ablation electrodes or imaging probes proximate specific tissues of interest.
To enable manipulation of the instrument, such as a catheter, inside the body, a number of mechanism may be used to selectively xe2x80x9csteerxe2x80x9d the distal tip of the catheter while the operator inserts the device into the body. One such mechanism is a slidable control wire mechanism which includes a pair of control wires that span the length of the catheter shaft, or body. The control wires have respective distal ends anchored to specific locations at the distal tip of the catheter body corresponding to predetermined deflectional movement. The proximal ends of the wires are mounted to a slider mechanism that responds to the operator by placing one of the wires in tension, pulling at the catheter end for deflection in a first direction, while simultaneously compressing, or buckling, the other wire. An example of such a catheter configuration incorporating such a control mechanism is found in U.S. Pat. No. 5,383,852, assigned to the assignee of the present invention, and herein incorporated by reference in its entirety.
Typically, the surgical instrument includes a handle component. Handles for deflectable tip instruments typically rely on the user to generate the force required to deflect the tip member in either direction, to maintain deflection, and to return the tip member to center after deflection. Devices which accomplish the foregoing are often referred to as having bidirectional steering. Sometimes, the tip member is only deflected in one direction and is relied upon to generate the force required to return the tip member to center. These devices are referred to as having unidirectional. In all of these conventional handle designs, the handle is a passive component. The handle does not generate any force, it merely delivers the force applied by the user.
When the distal end of the instrument body, e.g. catheter body, is deflected, a force is generated that tends to drive the distal end back to its straightened position. This is commonly referred to as a xe2x80x9creturn to centerxe2x80x9d force. This is usually not a desired effect, for in use, it is often convenient for the user if once the catheter body is deflected, it remains so without the continuing input of force from the user to counter the return to center force coming from the catheter body. Existing passive instrument designs have needed to rely on friction, ratchets, or other xe2x80x9cdragxe2x80x9d mechanisms for producing this counter effect. For example, one such counter mechanism uses a set screw included within the handle to hold the catheter body in various locations so as to prevent the distal end of the catheter body from straightening out when the physician releases the handle. The set screw generally applies a friction force to the operational components of the handle. The friction force applied to the handle components must, of course, be greater than the maximum force generated by the distal end of the catheter body. The maximum force is generated when the distal end is in its most curved orientation. One of the associated disadvantages of such counter mechanisms is that in order to achieve the required drag to maintain the shape of the catheter body, the force required to deflect the distal end may be inconvenient to the user. In other words, it may be difficult for many users to conveniently use a thumb or finger to manipulate the handle to cause deflection of the distal end because the force required to do so is too great.
U.S. Pat. No. 6,013,052 (""052) to Durham et al. discloses a catheter handle having a piston-type actuator device along with a biasing element which biases the piston in the distal direction. The ""052 patent is hereby incorporated by reference in its entirety. The device disclosed in the ""052 patent is of the type which has unidirectional steering. One of the associated disadvantages with this type of biasing mechanism is that the mechanism is only designed for use with unidirectional steering devices. In other words, the biasing mechanism counters only one direction one movement of the deflectable tip. As procedures become more complex and to permit greater latitude in performing the procedures, it is more desirable to use bidirectional devices in comparison with unidirectional devices. One of skill in the art will appreciate that it is significantly more difficult to provide an active counterforce mechanism for a device having bidirectional steering. One reason is that there is limited room in the housing to position a mechanism which can translate bidirectional movement into one direction on the control mechanism of the deflectable tip.
Therefore, those skilled in the art have recognized the need for a bidirectional mechanism to counter the return to center force generated by the deflected distal end such that the catheter body remains in a deflected state without the continuing input of force from the user while as the same time the force required to initially deflect the distal end is reasonable.
The present invention is directed to an assembly which provides an active handle for use in a steerable surgical instrument having a shaft deflectable in two directions (bidirectional steering). Typically, the surgical instrument includes a handle component which the user manipulates to cause a distal end of the instrument shaft to deflect in one of two directions. The distal end comprises an end tip portion of the shaft which extends outwardly from the handle. A control mechanism in accordance with the invention is preferably disposed within the handle and extends through the shaft for selectively controlling the direction and degree of deflection at the distal end in one of two directions. For example, one exemplary control mechanism uses control or steering wires to selectively deflect the distal end. The active counterforce mechanism according to the present invention is designed to be used in combination with the control mechanism and provides a force which counters the return to center force generated by the deflection of the shaft at the distal end thereof. Optimally, the active counterforce mechanism exactly balances the return to center force across the instrument""s deflection range. This results in the user experiencing little if any resistance during the manual manipulation of the control mechanism in either direction. This permits very low forces to be applied in order to deflect the distal end and also permits low forces to be applied in order to help the instrument maintain and xe2x80x9choldxe2x80x9d a particular deflection shape once the shaft is deflected. Accordingly, the handle is made to be an active rather than a passive component of the instrument because the handle itself generates a force via the counterforce mechanism to offset the return to center force generated by the deflected shaft as the shaft is deflected in either direction. In addition, the counterforce mechanism produces a variable force in that as the angle of deflection increases and the return to center force increases, the counterforce likewise progressively increases so as to balance the return to center force.
In one exemplary embodiment, the instrument comprises a bidirectional steerable catheter having a slider based control mechanism disposed within a handle housing. The user manipulates a thumb control linked to the slider for longitudinally displacing the slider within the handle housing. This action causes the steering wires or the like to deflect the distal end of the shaft in one of two directions.
According to a first embodiment, the active counterforce mechanism comprises a mechanical mechanism which includes a rotatable bell crank lever operably connected to a biasing element. The biasing element is also connected to the handle housing and the bell crank lever is connected to the slider using several pivotable members. The counterforce mechanism is designed so that when the slider and the shaft are in neutral positions (nondeflected), the counterforce mechanism provides no counterforce because of the absence of any return to center force. As the control mechanism and more specifically, the slider thereof, is manipulated by the user, the pivotable members pivot and cause the rotation of the bell crank lever. This results in the biasing element applying a force to the bell crank lever such that a counterforce is generated which balances the return to center force of the shaft. In other words, when the slider moves in either the proximal or distal directions, the biasing element applies a force to the bell crank lever which further directs the bell crank lever in the respective direction and prevents the bell crank lever from being forcedly rotated in the opposite direction as a result of the return to center force being applied thereto. The user thus is able to easily and continuously deflect the distal end through its deflection range in both directions using the slider and also a given deflection point may be held more easily due to balancing of the forces acting on the handle mechanisms.
In a second embodiment, the active counterforce mechanism comprises a pivotable cross bar assembly in which the biasing element is in the form of a leaf spring. The pivotable cross bar assembly is flexed outwardly in the either the proximal or distal directions depending upon the directional movement of the slider which is connected thereto using another cross bar. The leaf spring applies a force to the pivotable cross bar assembly so as to encourage and facilitate the outward flexing of the assembly though its range of motion. As in the first embodiment, the mechanism provides a counter force which balances the return to center force generated by the shaft as the shaft travels in one of two directions.
In a third embodiment, the active counterforce mechanism includes a roller assembly having a pair of rollers which travel across first and second track members disposed within the handle. The rollers are connected to linear arms of a torsion spring which is itself connected to the slider using a bar member. The torsion spring serves as the biasing element and generates a force which acts to push the rollers apart. The first and second track members are spaced apart from one another and each preferably includes a curved surface such that as the rollers travel to either end thereof, the torsion spring serves to force the rollers further apart from one another. The force of the torsion spring that is exerted on the slider is approximately zero in the neutral position but increases as the slider is moved and the rollers travel along the track members. This mechanism likewise generates a variable force which counters and preferably balances the return to center force as the slider is moved causing bidirectional movement of the deflectable tip.
It will be understood that there are a number of mechanisms that may be used in making an active type handle where the handle itself generates force instead of merely delivering force as in the designs of the conventional passive handles. In contrast, the active counterforce mechanism of the present invention converts the handle into an active component which generates force in response to the return to center force being generated by the bidirectional shaft. As the handle is used to deflect the instrument through its range, the force produced by the counterforce mechanism becomes progressively greater, to counter the return to center force. This provides assistance to the user in deflecting the distal end and in also maintaining or holding the distal end at a given angle of deflection. According to the present invention, the active counterforce mechanism translates slider movement in two directions into a single biasing direction of the biasing element. Advantageously, the active counterforce mechanism is intended for use with bidirectional devices and is designed to be disposed within the existing constraints on the handle housing.
Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.